Interpretive Summary: Brucellosis is a bacterial disease of livestock animals. It causes abortion and other problems that affect agricultural productivity and marketing. Brucellosis eradication has been mandated by congress and the program has been very effective. When a new outbreak of brucellosis occurs, it is important to quickly identify the origin of the infection to prevent additional spread. There are no tools available for differentiating most outbreak strains originating from livestock to wildlife. For many diseases, the RNA molecules needed for making protein have minor differences that can be used to identify bacterial strains. This study looked at these RNA molecules from the bacterium that causes brucellosis. We found that the RNA molecules are too similar to be used for differentiating the strains that cause brucellosis outbreaks.

Technical Abstract:
Brucella is a pathogenic bacteria of livestock animals. Rapid subtyping of Brucella field isolates would be very helpful to the brucellosis eradication programs in the USA and other countries. The ribosomal RNA operons (rrn) are often used as a target for bacterial typing. Other laboratories have studied portions of the Brucella rRNA operons, but to date no one has characterized a complete operon from Brucella. Nor has anyone studied the rRNA genes from a specific rrn copy. The present study characterizes all 3 Brucella melitensis rrn loci individually. All 3 operons are organized with a 593-bp conserved sequence followed by the 16S gene, an intergenic spacer containing tRNA-Ile and tRNA-Ala genes, the 23S gene, other intergenic spacer devoid of tRNA genes, the 5S gene, and an f-M NA gene. The DNA sequences of all 3 operons are identical over the entier 6359 bp region. The sequences diverge immediately after the f-Met tRNA but each contains an inverted repeat sequence that could function as rho-independent transcription terminators. The previously uncharacterized 23S genes were found to contain a 371-bp insertion 181-bp from the 5' end of the 23S gene. The location of the insertion matches intervening sequences (IVSs) forund in other Rhizobiaceae. The size and sequence of the Brucella IVS differs from previously reported IVS sequences. Of the IVS sequences described, the Agrobacterium vitis strain S4 IVS is the most similar to the Brucella IVS. A study of the distribution of the IVS sequence in other Brucella species showed that all Brucella species and biovars, including isolates obtained from marine mammals, contain the IVS in all 3 rrn operons. This lack of genetic diversity demonstrates that the rRNA operons are not appropriate targets for Brucella typing.